9,250 research outputs found
Nonlinear Gauge Transformations and Exact Solutions of the Doebner-Goldin Equation
Invariants of nonlinear gauge transformations of a family of nonlinear
Schr\"odinger equations proposed by Doebner and Goldin are used to characterize
the behaviour of exact solutions of these equations.Comment: 12 pages, LaTeX, to appear in "Nonlinear, Deformed and Irreversible
Quantum Systems", Proceedings of an International Symposium on Mathematical
Physics, World Scientific, Singapore 199
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
A simple model illustrating the impossibility of measuring off-shell effects
We consider a simple model and make use of field transformations in
Lagrangian field theories to illustrate the impossibility of measuring
off-shell effects in nucleon-nucleon bremsstrahlung and related processes.Comment: 3 pages, Latex2e, uses espcrc1.sty, contribution presented at the
16th International Conference on Few-Body Problems in Physics, Taipei,
Taiwan, 6-10 March 200
Generalized orientations and the Bloch invariant
Abstract. For compact hyperbolic 3-manifolds we lift the Bloch invariant defined by Neumann and Yang to an integral class in K3(C). Applying the Borel and the Bloch regulators, one gets back the volume and the Chern-Simons invariant of the manifold. We also discuss the non-compact case, in which there appears a Z/2-ambiguity
Reassessing Public Meetings As Participation in Risk Management Decisions
Using a U.S. case study, Ms. McComas and Dr. Scherer discuss how reliance on public meetings as tools for risk communication in public policy decisions affects relationships between stakeholders and risk managers
Interacting electrons on trilayer honeycomb lattices
Few-layer graphene systems come in various stacking orders. Considering
tight-binding models for electrons on stacked honeycomb layers, this gives rise
to a variety of low-energy band structures near the charge neutrality point.
Depending on the stacking order these band structures enhance or reduce the
role of electron-electron interactions. Here, we investigate the instabilities
of interacting electrons on honeycomb multilayers with a focus on trilayers
with ABA and ABC stackings theoretically by means of the functional
renormalization group. We find different types of competing instabilities and
identify the leading ordering tendencies in the different regions of the phase
diagram for a range of local and non-local short-ranged interactions. The
dominant instabilities turn out to be toward an antiferromagnetic spin-density
wave (SDW), a charge density wave and toward quantum spin Hall (QSH) order.
Ab-initio values for the interaction parameters put the systems at the border
between SDW and QSH regimes. Furthermore, we discuss the energy scales for the
interaction-induced gaps of this model study and put them into context with the
scales for single-layer and Bernal-stacked bilayer honeycomb lattices. This
yields a comprehensive picture of the possible interaction-induced ground
states of few-layer graphene.Comment: 12 pages, 12 figure
Strong Coupling Theory of Two Level Atoms in Periodic Fields
We present a new convergent strong coupling expansion for two-level atoms in
external periodic fields, free of secular terms. As a first application, we
show that the coherent destruction of tunnelling is a third-order effect. We
also present an exact treatment of the high-frequency region, and compare it
with the theory of averaging. The qualitative frequency spectrum of the
transition probability amplitude contains an effective Rabi frequency.Comment: 4 pages with 3 figure
Optimized time-dependent perturbation theory for pulse-driven quantum dynamics in atomic or molecular systems
We present a time-dependent perturbative approach adapted to the treatment of
intense pulsed interactions. We show there is a freedom in choosing secular
terms and use it to optimize the accuracy of the approximation. We apply this
formulation to a unitary superconvergent technique and improve the accuracy by
several orders of magnitude with respect to the Magnus expansion.Comment: 4 pages, 2 figure
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